Music synthesizer keyboard

ABSTRACT

THE INVENTION CONCERNS A MUSICAL KEYBOARD FOR PROVIDING A TWO-VOICED OUTPUT FROM A MUSIC SYNTHEISIZER. THE SYSTEM INCLUDES A VOLTAGE DIVIDER WHICH PROVIDES A PLURALITY OF VALUES OF POTENTIAL AND A PLURALITY OF SWITCHES EACH CONNECTED TO A DIVIDER TAP AT A UNIQUE ONE OF THE POTENTIAL VALUES. THE SIMULTANEOUSLY CLOSURE OF A PLURALITY OF SWITCHES APPLIES THE SELECTED VOLTAGE TO A PAIR OF VOLTAGE-CONTROLLED OSCILLATORS SO AS TO PROVIDE A TWO-VOICED OUTPUT DETERMINED BY THE TWO SELECTED VOLTAGES HAVING THE GREATEST AND LEAST ABSOLUTE AMPLITUDE VALUES.

April 23, 1974 R. E STEARNS Re. 27, 983

MUSIC SYNTHESIZER KEYBOARD Original Filed Dec. 17, 1970 VLTAGE BNTRDLLEDSCILLATOR UnitedY States Patent Oce Reissued Apr. 23, 1974 27,983 MUSICSYN'IHESIZER KEYBOARD Richard E. Stearns, Sharon, Mass., asslgnor to ARPInstruments, Inc., Newton, Mass.

Original No. 3,665,089, dated May 23, 1972, Ser. No. 99,193, Dec. 17,1970. Application for reissue Aug. 7, 1972, Ser. No. 278,190

Int. Cl. G10h 1/00 U.S. Cl. 841.01 6 Claims Matter enclosed ln heavybrackets [j appears ln the original patent but forms no part of thisreissue specification; matter printed in italics indicates the additionsmade by reissue.

ABSTRACT F THE DISCLOSURE The invention concerns a musical keyboard forproviding a two-voiced output from a music synthesizer, The systemincludes a voltage divider which provides a plurality of values ofpotential and a plurality of switches each connected to a divider tap ata unique one of the potential values. The simultaneous closure of aplurality of switches applies the selected voltage to a pair ofvoltage-controlled oscillators so as to provide a two-voiced outputdetermined by the two selected voltages having the greatest and leastabsolute amplitude values.

RELATED APPLICATION This invention is a reissue application of Pat. No.3,665,089 issued on May 23, 1972.

This invention relates to electronic musical instruments and moreparticularly to music synthesizers. The so-called music synthesizerscurrently available today are monophonic, i.e. only one note at a timemay be played. The usual keyboard system of these monophonicsynthesizers comprises a series string of precision resistors driven bya constant current source. For the normal musical scale, the circuitryis adjusted to produce a 1,42 volt drop across each resistor in thestring. Depression of a key connects a busbar to a point along theresistor string, applying the' voltage at that point to the input of abuffer amplifier (Unity gain follower). The latter, in turn, drives avoltage-controlled oscillator to the appropriate frequency for the keydepressed. If two keys are depressed simultaneously, only the notecorresponding to the lower frequency key will sound.

A primary object of the present invention is to provide a plural-voicedmusic synthesizer. Another object of the present invention is to providea synthesizer keyboard system capable of playing two notessimultaneously. Yet another object of the present invention is toprovide a keyboard system capable of simultaneously playing the twoselected notes corresponding to the highest and lowest frequency valuesignificance of the keys played.

The above objects, advantages, and features of the present invention, aswell as others, are accomplished by providing a music synthesizerkeyboard system for providing a plural-voiced output and comprisingmeans for providing a scaled sequence of signals of differing absolutevalues each corresponding to a respective key on said keyboard. Meansare also provided, responsive to the signals, such that simultaneousselection of more than one of the signals will provide a two-voicedoutput determined by the two selected signals having the greatest andleast absolute values.

Other objects of the invention will in part be obvious and will in partappear hereinafter. The invention accordingly comprises the apparatuspossessing the construction, combination of a elements, and arrangementof parts which are exemplified in the following detailed disclosure, andthe scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the presentinvention, reference should be made to the following detaileddescription taken in connection with the accompanying drawing wherein isshown a diagram of a network for use in a music synthesizer, partly inblock form and particularly schematic.

The drawing is essentially of a network in which a manually operablekeyboard is shown schematically within block 10 enclosed in brokenlines. Means are included for providing a plurality of signals ofdiffering absolute amplitudes, scaled preferably according to thefrequency relationships of the standard musical half tone scale. Thus,for example, one of the signals may correspond to A above middle C (or,as will be seen later, has an amplitude which ywill control anappropriate oscillator to produce the requisite audio frequency of 440cps) and other signals will then correspond to higher octaves orharmonics in which the A tone will be double, triple, etc. the lowerfrequency, as well-known in the art.

To this end there is provided a voltage divider comprising source 12,preferably of constant current, connected to a string of seriesconnected precision resistors 14, 15, 16, 17, and 18 scaled in ohrnicvalues to provide the desired signal relation by way of the voltage dropacross the resistors. The other end of the string of' resistors isgrounded or held at a fixed level. The number of resistors shown ismerely exemplary and preferably is one less than the number of signals(or tones) desired. The drawing illustrates five resistors and theresistor .string is broken to indicate that six additional resistors canbe provided for a full octave. To provide access to the Signals orvoltages thus provided, tap 19 is disposed between source l2 andresistor 14, and similar taps 20, 2l, 22, 23, and 24 are respectivelyprovided between resistors 14 and 15, resistors 15 and 16 resistors 16and 17, resistors 17 and 18, and at [ground or] some arbitrary level setby variable rheostat 25.

Connected to each of taps 19, 20, 21, 22, 23, and 24 is a. respectivekey-operated switch shown typically as mechanical single-pole, singlethrow switches 26, 27, 28, 29, 30, and 31, although any other type ofswitch can be employed as well. All of the output terminals of theseswitches are connected to a common bus 32 which in turn is connected tothe input of amplifier 33.

Tap 19 is also connected to the input of inverting amplifier 34. Source36 of reference potential is provided, and its output and the output ofamplifier 34 are connected together to inputs of summing circuit 38. Thoutput of summing circuit 38 is connected to an input of another summingcircuit 40. The output from amplifier 33 is likewise connected to aninput of summing circuit 40 through a buffer means such as amplifier 42.The output from summing circuit 40 is connected to the control input ofvoltage-controlled oscillator 44. The output of amplifier 33 isconnected to the control input of voltagecontrolled oscillator 46.Summing circuits 38 and 40, buffer amplifier 42, amplifiers 33 and 34,and voltagecontrolled oscillators 44 and 46 may be selected from any oneof a number of standard circuit configurations well-known in the art,and particularly the amplifiers and summing circuits can be appropriatetypes of wellknown operational amplifiers.

Operation of the electronic music system shown in the drawing will nowbe described. Source 12 supplies a preferably constant current tojunction 19 to which the string of series-connected resistors 14, 15,16, 17, and 18 of keyboard 10 is connected. These resistors provide anumber of different voltages at each of taps I9 20, 2l, 22, 23, and 24.Closure of one of switches 26, 27, 28, 29, 30, or 31 connects thecorresponding tap to bus 32 and thus applies the voltage at that tap tothe input of amplifier 33. For example, closure of switch 27 applies thevoltage at tap 20 to the input of amplifier 33.

Reference source 36 is selected to provide a potential of the sameabsolute amplitude as the voltage at the head of the divider (i.e. attap 19) but of the opposite polarity to the output of amplifier 34.Therefore, when only one switch, such as, for example, 27 is closed, theinput signals to summing circuit 38 are equal and opposite so the outputof circuit 38 is substantially zero. The voltage at tap 20, which isless than that at tap 19 by the IR drop across resistor 14, will thus beapplied both to the input of oscillator 46 directly from amplifier 33and to the input of oscillator 44 via amplifier 33, buffer amplifier 42,and summing circuit 40. Assuming that amplifier 42 and summing circuitexhibit a total gain of unity, oscillators 44 and 46 will have identicalinput signals and, if the oscillators too are identical, these inputsshould rprovide the same frequency outputs.

When any two switches of keyboard 1f] are closed simultaneously, theresistors between the two closed switches are shorted out, causing thevoltage at tap 19 to drop by an amount equal to the sum of the voltagedrops across each shorted resistor. This voltage appearing at tap 19 isapplied to amplifier 34 and then summed in summing circuit 38 togetherwith the voltage from reference source 36. The output from summingcircuit 38 will be the difference between the voltages from amplifier 34and source 36. Meanwhile, the voltage applied at the input of amplifier33 is the voltage from the tap of lowest voltage connected to anactuated switch. The output voltage from amplifier 33 is simultaneouslyapplied to oscillator 46 and via buffer amplifier 42 to summing circuit40 where it is summed together with the difference voltage from summingcircuit 38 to provide a voltage corresponding to the voltage from thetap of highest voltage connected to an actuated switch. This summedvoltage from summing circuit 40 is applied to oscillator 44. The resultis that the oscillator 44 will provide a frequency output correspondingto the actuated key for the higher note, and oscillator 46 will providea lower frequency output corresponding to the actuated key or switch forthe lower note.

For example, one may assume that the resistors in the voltage dividerand the output of the current source are such that the voltage dropacross the divider is one volt per octave of frequency of the output ofoscillator 46 and thus l/l2 volt across each resistor in the divider.One can also assume that the voltages thus switched by switches 26, 27,28, 29, 30, and 31 respectively are capable of generating in oscillator46 the audio frequencies in half tones from middle C down to G belowmiddle C. Lastly, assume that the normal voltage of current source 12 is+4 volts, the voltage from reference source 26 is +4 volts, that allamplification and summing is with unity gain. that only amplifier 34inverts and that oscillators 44 and 36 are identical.

The following table shows some examples of resulting outputs from thesimultaneous closing of two selected keyboard switches with the sameparameters given above. V1 is the voltage appearing at tap 19 upon thesimultaneous closure of the two switches. V2 is the voltage appearing atthe input of amplifier 33 upon the simultaneous closure of the same twoswitches. V2 is the voltage ap- TABLE I Closed switches Vi V: V44

2e 27 311/12 311/12 1/12 4 B. 2s 2s 31o/12 31u/12 2/12 4 B 2e 2s 3 9/123 9/12 3/12 4 A. 27 23 311/12 31o/12 1/12 311/12 B 27 29 31o/12 3 9/122/12 211/12 12 A. 2s 29 311/12 3 9/12 1/12 a 10,/12 Bilan.- 3 9/12 A.

It should be noted that the value of A is a direct measure of the numberof half-tones (in this example) between the two notes sounded and,referred to the voltage representing the note of lower frequency so asto be summed therewith, provides a summed voltage which then mustrepresent the note of higher frequency.

Adjustment of potentiometer 25 will result in shifting all of thevoltages at the various taps by the same amount, therefore, can be usedto tune a number of voltage divider systems to different octaves.

Since certain changes may be made in the above apparatus withoutdeparting from the scope of the invention herein involved, it isintended that all matter contained in the above description or shown inthe accompanying drawing shall be interpreted in an illustrative and notin a limiting sense.

What is claimed is:

1. In an electronic system, in combination:

means for providing a plurality of voltages of different values;

means for selecting at least two of said voltages substantiallysimultaneously;

means for providing a reference voltage;

means for deriving a difference signal from the values of said referencevoltage and one of the selected voltages;

means for deriving an output signal from the values of said differencesignal and the other of said selected voltages, and

means for generating two signals having frequencies in accordancerespectively with the values of said output signal and said other ofsaid selected voltages.

2. In a system as defined in claim 1, wherein said means for providingsaid plurality of voltages comprises a voltage divider, and said meansfor selecting comprises a plurality of switching means each having aninput terminal connected to a respective tap in said divider, the outputterminals of all of said switching means being connected to a commonbus.

3. In a system as defined in claim 2 wherein said difference signal isproportional to the voltage drop along said divider between the tapsclosest to opposite ends of said divider and connected to at least twocorresponding switching means in closed condition.

4. In a system as defined in claim 1 wherein said output signal is avoltage and said means for generating two signals comprises a pair ofvoltage-controlled oscillators.

5. Electronic musical apparatus comprising, in combination:

a voltage divider having a plurality of tags each adapted to have aunique voltage thereon selected in order from a set of voltage levelswhich progressively increase in said order from a predetermined initialminimum amplitude,

a like plurality of key-operated switches each having an input terminalconnected to a corresponding tap,

all output terminals of said switches being coupled to a common bus,

a source of reference voltage,

means for summing said reference voltage with a first signal derivedfrom the maximum voltage level 0n said tatps when one or more of saidswitches are closed so as to produce a difference signal;

first and second oscillators for providing output signals havingfrequencies variable in accordance with varations in respective controlsignals;

means for applying to said first oscillator a first control signalderived from the lowest voltage level of the taps connected to closedones of said switches;

means for summing said difference signal with said first control signalso as to derive a second control signal; and

means for applying said second control signal to said second oscillator.

6. Apparatus as defined in claim 5 wherein said dif- The followingreference, cited by the Examiner, are of record in the patented file ofthis patent or the original patent.

References Cited UNITED STATES PATENTS 3,288,904 ll/I966 George 84-1.0I

RICHARD B. WILKINSON, Primary Examiner U. WELDON, Assistant ExaminerU.S. C1. X.R. 84-l.17, 1.24

